Coaxial magnetron having anode vanes with notches thereon for reducing the frequency of operation



March 25, 1969 w. A. GERARD 3,435,285

COAXIAL MAGNETRON HAVING ANODE VANES WITH NOTCHES THEREON FOR REDUCING THE FREQUENCY OF OPERATION Filed April 1. 1966 7/21 5 1/2! 2! 24 I5i 24- *1! P U INVENTOR William A. Gerard United States Patent ice US. Cl. 31539.77 6 Claims ABSTRACT OF THE DISCLOSURE A coaxial magnetron in which the anode vanes are provided with rectangular notches on the edge portions of the anode vanes to reduce the necessary length of the anode vane over conventional unnotched anode vanes for a given frequency and thereby make the magnetron more compact in size without effecting the electrical or thermal characteristicsof the magnetron.

This invention relates to magnetrons and more particularly to coaxial type of magnetrons.

In the R. J. Collier and J. A. Feinstein US. Patent 2,854,603, issued Sept. 30, 1958, there is disclosed a coaxial magnetron structure which comprises an inner and outer resonant system. The inner resonant system in cludes a cylindrical anode together with a plurality of anode vanes radially extending inwardly therefrom. These vanes define a circumferential array of inner, or anode cavity resonators surrounding a cathode. An outer cavity resonator is defined between an outer wall and the cylindrical anode. The two systems are coupled by a circumferential array of uniformly spaced slots through the cylindrical anode which connects the outer resonant system with the anode cavity resonators. The inner resonant system is designed to oscillate in the 1r mode, while the outer system is designed to oscillate in the TE mode. The two systems are efiectively locked together by means of the coupling slots.

Such a structural arrangement overcomes many disadvantages inherent in magnetrons of prior design. The conventional magnetron does have an advantage over the coaxial magnetron in that the heat problem is easier to handle. The anode vanes in the conventional magnetron are connected directly to an external wall. This provides a short thermal path from the anode vane tips to the heat radiating fins. The coaxial magnetrons are also normally larger than their equivalent conventional magnetrons. It is important that weight and size be reduced to a minimum in most aircraft applications. One possible way of reducing the size is to reduce the length of the anode vane. The vanes act as quarterwave transformers which provide a high RF voltage between vanes near the cathode for interaction with the electrons. The frequency of the coaxial magnetron is determined by the inductance and capacitance incorporated within both the inner and outer resonant systems although the outer system is the principal frequency determining member. The efiiciency of the generation of electrical oscillations in the inner system is determined by the inductance and capacitance incorporated therein as a function primarily of the geometry of the physical elements making up the aforementioned anode cavity resonators. Each of the cavity resonators has a distributed capacitance and inductance. The inner portion of the cavity resonator, adjacent the cathode, is predominantly capacitance. The inductance is concentrated in the outer portion of the cavity resonator, that is the portion farthest removed from the cathode.

3,435,285 Patented Mar. 25, 1969 It is accordingly an object of this invention to provide an improved coaxial magnetron structure.

It is another object of this invention to provide a magnetron of smaller dimension over conventional coaxial magnetrons by reduction of the vane length.

It is another object to provide an improved anode vane for a given wavelength coaxial magnetron reduced in length from the prior art coaxial magnetron anode vanes.

It is another object of this invention to provide means for shortening the anode vane in a manner that facilitates manufacture of the resulting tube.

Briefly, the present invention provides an improved coaxial magnetron of smaller dimensions than prior art coaxial magnetrons by providing rectangular notches in the edge portions of the anode vanes and particularly in the portion of the cavity resonator so as to affect the inductance portion of the cavity resonator.

These objects and advantages of the present invention will become more apparent when considered in view of the following detailed description and drawings, in which:

FIGURE 1 is a view of a coaxial magnetron partly in section and incorporating the teachings of this invention; and

FIG. 2 is an enlarged sectional view of the anode shown in FIG. 1.

With reference now to the drawings, there is shown a coaxial magnetron embodying the present invention. A magnetron is comprised of a body or shell member 10 which is substantially cup-shaped. The body 10 includes an outer wall member 12 forming the outer wall of an outer cavity resonator 30 and a bottom wall member 14 forming the lower Wall of the cavity resonator 30. The body member 10 is of a suitable electrically conductive material such as copper. An upper end plate 16 also of copper provides the upper wall of the cavity resonator 30.

Output energy from the magnetron is derived from the cavity resonator 30 by means of suitable coupling means 18. A plurality of heat radiating fins 13 are provided on the outer Wall 12 of the cavity resonator 30 and a suitable cooling medium such as air may be directed over the radiating fins 13.

An anode 20 is provided within the body member 10. The anode 20 includes a cylindrical member 23 which defines the inner wall of the cavity resonator 30. The cylindrical anode member 23 is secured to the lower plate 14. The cylindrical anode member 23 is secured by a flexible member 15 to the upper end plate 16. In this manner, the member 15 which is of a good thermal conductivity material such as copper permits heat conduction from the anode 20 while still permitting expansion of the anode 20. The anode 20 includes a plurality of vanes 24 which extend radially inwardly from the cylindrical member 23 and define a plurality of anode cavity resonators 29. Centrally disposed and extending through apertures in the end plate 16 and the bottom plate 14 is a cathode sleeve 26 which is provided with an electron emissive coating 28 of a suitable material such as barium oxide.

The magnetic circuit of the magnetron includes an exhaust pole piece 27 extending through the aperture provided in the upper plate 16 and a cathode pole piece 32 extending through an aperture in the bottom plate 14. Two suitable permanent magnets (not shown) generally of a horseshoe configuration are provided and are secured to the pole pieces 27 and 32 to provide a magnetic field within the interaction region. This magnetic field is perpendicular to the electron path from the cathode 0 coating 28 to the anode 20.

The anode cylinder 23 includes a plurality of slots? 21 arranged parallel to the axis of the tube and to the cathode sleeve 26 and the slots extend from substantially adjacent the end cover 16 to the bottom plate 14. In the specific device shown, the slots 21 are provided in alternate anode cavity resonators 23.

Referring in detail to FIG. 2, there is shown an enlarged view of the anode vane 24 which has a length of .220 inch and a height of .330 inch. A notch 50 is provided in each edge of the anode vane 24 having a notch width of .050 inch and a depth of .020 inch and spaced at a distance of .020 inch from the cylindrical anode wall 23. It is obvious that the notch 50 could be provided at only one end if so desired and still obtain a reduction in the operating frequency without increasing the length of the anode vanes. For example, with the dimensions given above a reduction in frequency of 170 megacycles was obtained in an X-band mode. The X-band mode is within the frequency range of 8.5 6H to 9.6 6H The notch 50 is located in the outer portion of the cavity resonator 23 that is predominantly inductance. It is found that the inductive portion is that portion remote from the cathode 28. In the specific example given, the notch 50 is located within the outer half of the vane 24. By providing the notch 50 within the outer half of anode cavity resonator 23, the inductance of the cavity is increased and therefore the frequency decreased.

The resulting anode vane 24 provides a good thermal conductor for removing heat from the anode tips and also the rectangular type notch 50 provides a structure that is easy to manufacture. With this anode vane, fiat areas remain even though there may be burrs on the corner thus facilitating quality control of the part. It should be noted that the radius or burr itself does not cause error alone, but leads to errors in measuring the critical parts of the vane.

Various modifications may be made within the spirit of the invention.

I claim as my invention:

1. A coaxial unstrapped magnetron comprising a centrally located cathode, a tubular anode Wall member surrounding said cathode, a plurality of vanes extending inwardly from the inner surface of said anode wall toward said cathode and forming a plurality of inner cavity resonators and an interaction space adjacent and concentric with said cathode capable of oscillation in the 1r mode, an external cavity resonator encompassing said inner cavity resonators and including said anode Wall member capable of oscillation in the TE mode, said anode having coupling slots from selected inner cavity resonators to said external cavity resonator, each of said vanes having an inner edge adjacent said cathode and an outer edge secured to said wall member and upper and lower edges, each of said vanes having a notch in one of said upper and lower edges for reducing the frequency of operation.

2. A coaxial magnetron as defined in claim 1 in which said notch is substantially rectangular in shape.

3. The coaxial magnetron defined in claim 1 in which said notch is located in the high inductance portion of said inner cavity resonators.

4. A coaxial magnetron as defined in claim 1 in which said notch is located in the upper or lower edge portion adjacent the outer edge of said vane.

5. A coaxial magnetron as defined in claim 1 in which said notch is located within the upper or lower edge portion of said vane and within one-half of the distance from the outer edge of the vane.

6. A coaxial magnetron as defined in claim 2 in which said rectangular notch is located within the region adjacent the outer edge of the vane.

References Cited UNITED STATES PATENTS 3/1950 Pierce 315-39.6l X 9/ 1952 Powers 3l5-39.77 X

US. Cl. X.R. 

